This invention relates to multi-piece golf balls of at least three layers including a solid core, an intermediate layer and a cover, which are improved in feel, control and flight performance.
In the past, a variety of improvements were made on wound golf balls and solid golf balls. One typical attempt is to optimize the gage and hardness of the core and cover of a two-piece solid golf ball.
While most prior art solid golf balls have a two-layer structure consisting of a solid core and a cover, the recent trend has moved to a multilayer structure having an intermediate layer disposed between the solid core and the cover. Many attempts have been made to optimize the respective layers. For instance, JP-A 9-313643 discloses a three-piece golf ball which is improved in flight performance, durability, feel and controllability by optimizing the hardness distribution of the core alone and the overall hardness distribution of the ball including the core, intermediate layer and cover.
Also, JP-A 10-305114 discloses a multi-piece golf ball which is improved in flight performance and feel by optimizing the hardness balance among the core, intermediate layer and cover as well as the dimples.
Nowadays, golf players have a variety of diverse requirements, and further improvements in feel, controllability and flight performance are needed.
An object of the invention is to provide a multi-piece golf ball of at least three layers including a solid core, an intermediate layer and a cover, which is improved in feel, controllability and flight performance.
Regarding a golf ball comprising a solid core, an intermediate layer and a cover, the inventor has attempted to use a heated mixture of any one of the following compositions (1), (2) and (3) and having a melt index of at least 1 dg/min as the material of which the intermediate layer and/or the cover is made.
Composition (1) comprising the following:
(a) 100 parts by weight of an olefin-unsaturated carboxylic acid random copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a) and (b).
Composition (2) comprising the following:
(d) 100 parts by weight of a metal ion-neutralized olefin-unsaturated carboxylic acid random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (d) and (b).
Composition (3) comprising the following:
100 parts by weight of a mixture of (a) an olefin-unsaturated carboxylic acid random copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer and (d) a metal ion-neutralized olefin-unsaturated carboxylic acid random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a), (d) and (b).
It has been found that the multi-piece golf ball whose intermediate layer and/or cover is formed of the above-formulated material is improved in rebound and flight distance. This improvement in rebound leads to the advantage that there is left a room for further improvements in feel and controllability.
Continuing investigations in order to take the advantage to a full extent, the inventor has found that the improvement in rebound contributes to a softening of feel, and with respect to controllability, the same allows the cover to be softened so that an increased spin receptivity is expectable.
More specifically, the hardnesses of the respective layers of the multi-piece golf ball are such that the intermediate layer has a Shore D hardness of 40 to 63, the cover has a Shore D hardness of 45 to 68, the Shore D hardness of the solid core at its center is not greater than the Shore D hardness of the intermediate layer, which is not greater than the Shore D hardness of the cover. When the ball is hit, the ball receives the impact force over its entirety, rather than local concentration of the impact force, so that the energy loss associated with ball deformation is minimized. This leads to good rebound or restitution, an increase of travel distance and a soft feel. Additionally, the cover can be made so soft that spin receptivity is increased to provide for good controllability. The present invention is predicated on these findings.
In a first aspect, the invention provides a multi-piece golf ball comprising a solid core, an intermediate layer enclosing the solid core, and a cover enclosing the intermediate layer, wherein
at least one of the intermediate layer and the cover is formed of a heated mixture comprising
(a) 100 parts by weight of an olefin-unsaturated carboxylic acid random copolymer or an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer or both,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a) and (b), the heated mixture having a melt index of at least 1.0 dg/min,
the intermediate layer has a Shore D hardness of 40 to 63, the cover has a Shore D hardness of 45 to 68, the Shore D hardness of the solid core at its center is not greater than the Shore D hardness of the intermediate layer, which is not greater than the Shore D hardness of the cover.
In a second aspect, the invention provides a multi-piece golf ball comprising a solid core, an intermediate layer enclosing the solid core, and a cover enclosing the intermediate layer, wherein
at least one of the intermediate layer and the cover is formed of a heated mixture comprising
(d) 100 parts by weight of a metal ion-neutralized olefin-unsaturated carboxylic acid random copolymer or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer or both,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (d) and (b), the heated mixture having a melt index of at least 1.0 dg/min,
the intermediate layer has a Shore D hardness of 40 to 63, the cover has a Shore D hardness of 45 to 68, the Shore D hardness of the solid core at its center is not greater than the Shore D hardness of the intermediate layer, which is not greater than the Shore D hardness of the cover.
In a third aspect, the invention provides a multi-piece golf ball comprising a solid core, an intermediate layer enclosing the solid core, and a cover enclosing the intermediate layer, wherein
at least one of the intermediate layer and the cover is formed of a heated mixture comprising
100 parts by weight of a mixture of (a) an olefin-unsaturated carboxylic acid random copolymer or an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer or both and (d) a metal ion-neutralized olefin-unsaturated carboxylic acid random copolymer or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer or both,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a), (d) and (b), the heated mixture having a melt index of at least 1.0 dg/min,
the intermediate layer has a Shore D hardness of 40 to 63, the cover has a Shore D hardness of 45 to 68, the Shore D hardness of the solid core at its center is not greater than the Shore D hardness of the intermediate layer, which is not greater than the Shore D hardness of the cover.
In one preferred embodiment, the solid core is formed of a polybutadiene-based rubber composition and has a diameter of 33 to 41 mm and a deflection of 2.5 to 7.0 mm under an applied load of 100 kg.
In another preferred embodiment, the intermediate layer has a gage of 0.3 to 3.0 mm, the cover has a gage of 0.3 to 3.0 mm, and the total gage of the intermediate layer and the cover is at least 1.0 mm.